Default personality?

Zimbra allows me to change the "from" address from the default personality but when I send mail it uses the account's default e-mail address, not the address I changed to. Is this a bug or by design?

I can also add a personality with a different e-mail address and send from that personality and it works correctly. However, I can't find any way to change the default personality to use when composing new mail. Is there any way to set the default compose personality to something other than the primary personality?

I'm trying to use this with a Yahoo account. On the Yahoo web interface, I'm actually able to set the default from address to other than the account's primary e-mail address, but Zimbra doesn't appear to honour this.